Xamarin.Forms 如何从 WCF 读取 json？

Question

I'm trying to create my first Xamarin.Forms mobile app with a map and pins, so please bear with me.

I'm trying to add pins to the map. I use this code to add one pin:

map = new Map { 
    IsShowingUser = true,
    HeightRequest = 100,
    WidthRequest = 960,
    VerticalOptions = LayoutOptions.FillAndExpand
};

map.MoveToRegion (MapSpan.FromCenterAndRadius (
    new Position (36.9628066,-122.0194722), Distance.FromMiles (3)));

var position = new Position(36.9628066,-122.0194722);
var pin = new Pin {
    Type = PinType.Place,
    Position = position,
    Label = "Santa Cruz",
    Address = "custom detail info"
};
map.Pins.Add(pin);

Now, instead of adding just one pin, I'd like to add several pins from a tsql table.

So I created a WCF service that returns a list of coordinates. One returns a json and the other returns a datatable :

public DataTable ToEraseGetCoordinates()
{
    string sqlQuery = "select lat,lon from MyStores";
    string connString = GetConnString();
    SqlDatabase sqlDatabase = new SqlDatabase(connString);
    DataSet result = sqlDatabase.ExecuteDataSet(CommandType.Text, sqlQuery);
    return result.Tables[0];
}
public System.IO.Stream ToEraseGetCoordinatesJson()
{
    string sqlQuery = "select lat,lon from MyStores";
    string connString = GetConnString();
    SqlDatabase sqlDatabase = new SqlDatabase(connString);
    DataSet result = sqlDatabase.ExecuteDataSet(CommandType.Text, sqlQuery);
    return ConvertToJson(result.Tables[0]);
}

I invoke the WCF like so: http://80.102.51.381:101/Service1.svc/ToEraseGetCoordinates (for an xml representation of the datatable)

For the JSON: http://80.102.51.381:101/Service1.svc/ToEraseGetCoordinatesJson , which returns this:

{"lat":25.7616,"lon":-80.1917},{"lat": 28.5383,"lon":-81.3792}

My question is: what do I next so that my Xamarin.Form reads this?

Regardless of the return type, I don't know how Xamarin will consume the WCF and draw the pins.

Answer 1

This earthquake map sample does basically what you want (it's a bit old, sadly).

Basically you want to download your Json (eg in this class )

// your http://80.102.51.381:101/Service1.svc/ToEraseGetCoordinatesJson would go here
var response = await client.GetAsync("earthquakesJSON?north=44.1&south=-9.9&east=-22.4&west=55.2&username=bertt");
var earthquakesJson = response.Content.ReadAsStringAsync().Result;

then you need to convert the Json - but you said you've already done that

var rootobject = JsonConvert.DeserializeObject<Rootobject>(earthquakesJson);

lastly just create and add the pins to the map

var earthquakes = await webSvc.GetEarthquakesAsync();
Xamarin.Forms.Device.BeginInvokeOnMainThread( () => {
    Debug.WriteLine("found " + earthquakeString.Length + " earthquakes");
    label.Text = earthquakeString.Length + " earthquakes";
    foreach (var earthquake in earthquakes)
    {
        var p = new Pin();
        p.Position = new Position(earthquake.lat, earthquake.lng);
        p.Label = "Magnitude: " + earthquake.magnitude;
        m.Pins.Add(p);
    }
});

Originally the pins weren't able to be databound, which is why it loops through to add them. Not sure if the ability to databind pings has been added to Xamarin.Forms since.

You'll probably want to keep track of the lat/longs so you can calculate a new region to set the maps view, to default to showing all the pins you added...

See the Maps docs and maps custom renderers for more info.